Evacuated or evacuatable blood-sampling tubes generally have a hollow cylindrical vessel, e.g. of glass or possibly of synthetic resin, which may be surmounted by a removable cap.
These tubes can be used with a blood-sampling device whose hollow cylindrical holder is equipped with a double-pointed needle, one point of which is inserted into a blood vessel of the patient while the other point is thrust through the self sealing membrane of the sampling tube when the latter is forced into the holder
The suction applied by the vacuum in the tube draws the blood into the latter.
The open end of the tube is closed by a cap which can hold in place a preferably constant wall thickness foil covering a portion of the cap and retained by a heat-sealable layer, and the self-sealing elastomeric membrane, e.g. of silicone rubber.
The foil is preferably of aluminum and forms the laminate with the heat sealing adhesives.
A sampling tube for a vacuum blood sampling system is described in German patent document-open application DE-OS No. 29 08 819. The closure element is here formed by a screw cap which has an opening and whose end presses the membrane of a self sealing material adapted to be pierced by the needle against the mouth of the tube.
This sampling tube requires that screw threads be provided both on the open end of the tube and on the cap. Moreover, the application of the cap by screwing it onto the tube must be carried out with care to ensure that the membrane will seal properly against the tube and the cap.
Access to the contents of the tube requires the time-consuming and tedious unscrewing of the cap.
Furthermore, with this system, one cannot readily detect whether or not the tube has been tampered with, i.e. opened in a manner unintended by the physician or the test laboratory. Finally it has been found that, with long storage, especially when the tubes are constituted or microporous plastic, there may be a failure of the vacuum within the tube.
Even a cap which has a flange upon which the closure element is applied by means of the heat sealable layer and wherein the sealing membrane lies outside the closure element but within the cap, is not always satisfactory. While such caps are effective in use, they pose problems of fabrication, particularly in making and storing the caps and or closure elements.